Schedule I - Condensed Parent Company Finanical Statements (Details-Comprehensive Income Statement) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Expenses:
Other operations and maintenance									$ 167,989	$ 164,478	$ 161,703
Total Operating Expenses	$ 114,967	$ 90,190	$ 93,364	$ 117,996	$ 108,795	$ 94,618	$ 98,077	$ 138,283	416,517	439,773	481,754
Operating Income (Loss)	23,958	46,527	28,212	29,531	22,178	46,177	24,049	31,851	128,228	124,255	138,098
Equity earnings from investment in ATC									8,428	7,728	9,150
Income before income taxes									118,073	112,706	128,504
Income tax provision	(7,570)	(15,714)	(9,284)	(9,945)	(7,417)	(15,351)	(8,008)	(10,587)	(42,513)	(41,363)	(48,185)
Net Income	$ 14,502	$ 27,880	$ 16,150	$ 17,028	$ 11,232	$ 28,354	$ 13,479	$ 18,278	75,560	71,343	80,319
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Unrealized (loss) gain on available for sale securities, net of tax									(155)	(101)	81
Comprehensive Income									75,405	71,242	80,400
MGE Energy [Member]
Operating Expenses:
Other operations and maintenance									720	690	689
Total Operating Expenses									720	690	689
Operating Income (Loss)									(720)	(690)	(689)
Equity earnings from investment in ATC									75,581	71,306	81,811
Other income/(loss), net									435	526	(1,879)
Other interest									176	136	93
Income before income taxes									75,472	71,278	79,336
Net Income									75,560	71,343	80,319
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Unrealized (loss) gain on available for sale securities, net of tax									(155)	(101)	81
Comprehensive Income									$ 75,405	$ 71,242	$ 80,400